The present invention is directed to a die hemming assembly and method, and in particular to a hemming assembly and method that utilize a vertical motion as part of the pre-hemming operation.
In the prior art, it is well known to join together a pair of preformed parts into a single unitary structure. This joining is particularly prevalent in the automotive industry where a component such as a hollow door, hood, deck gate, end gate, trunk lid or the like is formed using these joining techniques. Typically, these components comprise an outer and an inner panel. The edges of the panels are clinched together using a hemming machine or apparatus.
A widely-used process for hemming of door panels involves a pre-hemming step followed by a final hemming step. In the pre-hemming step, an upstanding or right-angled flange of one panel is bent over a flat edge of another panel by a pre-hemming die surface. In the final hemming step, the bent flange is flattened onto the flat edge of the other panel to form the hem using a final hemming die surface.
Various types of machines have been proposed to perform these types of hemming operations. One type uses a vertically-driven main die and a horizontally-driven hem gate. The hem gate supports the pre-hemming and final hemming die surfaces and is moved laterally or horizontally for hemming. The main die is raised vertically for the hemming steps. These horizontally-driven gates lack accuracy and repeatability in the hemming process. In these machines, there are typically four separate assemblies to hem each side of a rectangular or square unit. Since each assembly may have its own main die and drive for the hemmers, the overall apparatus is rather clumsy and bulky.
Another type of hemming machine uses a linkage and a swing-type motion to allow the pre-hemming and final hemming surfaces to contact the flange for hemming. The complicated drive mechanisms associated with these machines make them expensive and can cause unwanted variations over time in hemming performance.
Another hemming apparatus is disclosed in U.S. Pat. No. 5,150,508 to St. Denis. This patent discloses a hemming machine using the horizontally-driven hem gate and vertically-driven main die described above. In St. Denis, the main die is raised hydraulically between two positions for pre-hemming and final hemming. A lifter is used to then remove the hemmed part or load a unit to be hemmed. This machine also suffers from the drawbacks noted above.
Another problem with present day hemming apparatus that employ a swinging mechanism for pre-hemming is distortion to the panel. Referring now to FIGS. 1a and 1b, a pre-hemming operation is schematically depicted wherein panel 1 is hemmed to panel 3 using die 2. The arrow in FIG. 1a represents the motion of the pre-hemming tool (not shown), which would contact the end portion 5 of panel 1. FIG. 1b shows the panels in the pre-hemmed state with the end portion 5 bent over the edge 7 of the panel 2. Reference numeral 9 shows that lifting and distortion can occur at the bend 11 when the end portion is pre-hemmed using a swinging motion from the pre-hem tool. This lifting and distortion compromises the quality of the hemmed panels, and can result in part rejection.
In light of the disadvantages of prior art hemming machines, particularly the distortion at the hemmed edge when using swinging or arcuate pre-hemming motions, a need has developed to provide improved hemming apparatus and methods. The present invention responds to this need by providing a hemming apparatus employing a pre-hemming mechanism that employs a vertical pre-hemming action, and a pre-hemming mechanism that also cooperates with a vertical final hemming action.
It is a first object of the present invention to provide an improved hemming apparatus.
Another object of the present invention is to provide an improved method of hemming parts together.
Yet another object of the invention is a hemming apparatus employing a mechanism utilizing a generally vertical force for pre-hemming.
A further object of the invention is a method of hemming panels together wherein pre-hemming is primarily accomplished by a generally vertical action rather than a horizontal or arcuate motion.
A still further object of the invention is the ability to incorporate a number of pre-hemming and final hemming operations in sequence using a single downward motion of the hemming apparatus.
Other objects and advantages of the present invention will become apparent as a description thereof proceeds.
In satisfaction of the foregoing objects and advantages, the present invention provides a die hemming assembly which is improved over prior art types utilizing arcuate pre-hemming motion. The assembly includes components that make up a hemming apparatus, the apparatus adapted for hemming an upstanding edge of a first panel to an edge of a second panel to form a joint. The assembly includes a main die supporting the first and second panels, a pre-hem slide supporting a pre-hem tool that has an angled tool surface, and a final hem die holder supporting a final hem tool. A guide mechanism is in engagement with the pre-hem slide to direct the pre-hem slide along a first path generally vertical to the upstanding edge and along a second path angled with respect to vertical. At least one drive directs the pre-hem slide along the first and second paths and directs the final hem die holder along a generally vertical path. One drive can move both the pre-hem tool and the final hem die, either together or sequentially, or each can have their own drive.
A number of assemblies can be arranged together to hem a number of different edges, either in sequence or simultaneously. The various tools and dies can be appropriately spaced so that, if desired, one press or downward motion cycle can hem all the desired edges.
In one embodiment, the guide mechanism comprises an elongated element having at least one vertical guide surface and at least one angled guide surface. The pre-hem slide has at least one complementary vertical guide surface and at least one complementary angled guide surface. Movement of the at least one complementary vertical guide surface of the-pre-hem slide against the at least one vertical guide surface of the guide member directs the pre-hem tool generally vertically against the upstanding edge for at least a partial pre-hemming. Movement of the at least one complementary angled guide surface of the pre-hem slide against the at least one angled guide surface of the guide member angles the pre-hem tool away from the pre-hemmed edge to complete pre-hemming or permit final hemming.
The guide mechanism of this embodiment includes a horizontal guide to maintain a horizontal orientation of the pre-hem slide during angling movement. The horizontal guide can be a rail linked to the drive, and a set of roller bearings or the like linked to the pre-hem slide. The bearing follow in the rail as the pre-hem slide angles away from the edges to maintain the pre-hem slide in its horizontal orientation.
The main die is supported by a base, which with the main die forms a space to receive the pre-hem slide during its angled movement, thus allowing exposure of the pre-hemmed edges for final hemming.
The invention also entails a method of hemming at least one upstanding edge of one panel to the edge of another panel, whereby the upstanding edge is at least partially pre-hemmed by contacting the upstanding edge with a pre-hem tool that follows a generally vertical path. Completion of the pre-hemming can be accomplished by additional travel of the pre-hem tool along the vertical path, or by the pre-hem tool as it angles away from the edges to permit final hemming. Final hemming occurs by a final die traveling along a vertical path as well.
In one mode, the pre-hem tool is mounted on a slide body, and the slide body moves vertically and then at an angle as part of the pre-hemming and final hemming operations.
Once the pre-hemming and final hemming steps are complete, the die holder and pre-hem slide are moved back to their respective start positions to start the cycle all over again. A number of hemming operations can be performed in sequence using a number of the assemblies, whereby the pre-hem slides and final die holders would be arranged and spaced vertically apart so that a single downward stroke of the apparatus would complete the pre-hemming and final hemming for a number of edges of a pair of panels.